Reid (D-Nev.) said in a letter sent to Comey that his disclosure to Congress, made 11 days before the election, might have violated the Hatch Act, which prohibits partisan politicking by government employees.

“Your actions in recent months have demonstrated a disturbing double standard for the treatment of sensitive information, with what appears to be a clear intent to aid one political party over another,” Reid wrote. “I am writing to inform you that my office has determined that these actions may violate the Hatch Act, which bars FBI officials from using their official authority to influence an election. Through your partisan actions, you may have broken the law.”

The campaigns of Hillary Clinton and Donald Trump, including their respective running mates Tim Kaine and Mike Pence, reacted on Oct. 30 to the FBI's announcement that it will examine newly discovered Clinton emails. (Bastien Inzaurralde/The Washington Post)

While many Democrats and some Republicans have cast doubt on Comey’s actions, citing Justice Department policies and precedent on handling investigations ahead of elections, Reid’s letter is the most forceful denunciation leveled by a high-ranking elected official.

In the letter, Reid drew a contrast between how Comey has treated the Clinton email probe and how he has handled what Reid described as “explosive information about close ties and coordination between Donald Trump, his top advisors, and the Russian government.”

“The public has a right to know this information,” Reid said. “I wrote to you months ago calling for this information to be released to the public. There is no danger to American interests from releasing it. And yet, you continue to resist calls to inform the public of this critical information. By contrast, as soon as you came into possession of the slightest innuendo related to Secretary Clinton, you rushed to publicize it in the most negative light possible.”

The intelligence community has publicly accused Russia of attempting to interfere in the U.S. election by hacking political organizations and carrying out related acts. But it has made no statement on links between Russia and Trump or his campaign.

Richard W. Painter, a law professor at the University of Minnesota and the chief ethics lawyer in the George W. Bush White House from 2005 to 2007, wrote in a New York Times op-ed Sunday that he has filed a Hatch Act complaint against Comey with the federal Office of Special Counsel and Office of Government Ethics.

“We cannot allow F.B.I. or Justice Department officials to unnecessarily publicize pending investigations concerning candidates of either party while an election is underway,” Painter wrote. “That is an abuse of power. Allowing such a precedent to stand will invite more, and even worse, abuses of power in the future.”

But Georgetown University law professor David Vladeck, who is critical of Comey’s handling of the Clinton investigation, said that he did not believe that Comey had violated the Hatch Act.

“I do not think he has committed a crime,” said Vladeck, who was referring to Comey’s handling of the email probe, not Reid’s claims about Trump’s links to Russia. But, he added, “I do think he has abused his office.”​

​“Prosecutors have no warrant to characterize the behavior of someone not charged with a crime,” Vladeck said. “And it is grossly inappropriate for a prosecutor to fan political flames when there is no basis to even suggest any unlawful conduct.”

Current and former officials could not understand how Comey could send the letter without knowing if, for instance, any of the emails were marked “classified” or if they were duplicates of those already in the FBI’s possession.

Democrats fear that Comey’s disclosure could affect not only the presidential race but also tight congressional races down the ballot. Republican House and Senate candidates have seized on the news to pressure their Democratic opponents to break with Clinton. Reid is retiring from the Senate in January, and he has vowed to return Democrats to the Senate majority after two years in the minority.

In closing the letter, Reid told Comey that he has “been a supporter of yours in the past.”

“When Republicans filibustered your nomination and delayed your confirmation longer than any previous nominee to your position, I led the fight to get you confirmed because I believed you to be a principled public servant,” he said. “With the deepest regret, I now see that I was wrong.”